The present application claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2011 101 303.6, filed May 12, 2011, the entire disclosure of which is herein expressly incorporated by reference.
Exemplary embodiments of the present invention relate to an impact protection plate for mounting on the structure of a vehicle, in particular an aircraft.
Military transport aircraft, for example, the C160 Transall, are being increasingly used for humanitarian aid and disaster relief operations in crisis areas. In carrying out these operations, landings on unpaved runways are not uncommon, since the infrastructure in the affected countries, in particular in the region of the takeoff and landing strips, is often inadequately developed. These outlandings result in increased stone chip damage to the underside of the fuselage and to the antennas and valves located there. Stone chips to the antennas often have adverse effects on flight safety since proper functionality of navigation and radio devices may no longer be ensured due to the damage. In addition, these stone chips often result in high repair costs. For flights under icy conditions, propeller aircraft are also endangered by the impact of pieces of ice which come loose from the propeller.
German Patent Publication No. DE 10 2007 038 634 B3 describes an impulse-absorbing component as part of the structure of an aircraft, having a first wave-shaped, impulse-absorbing layer and a smooth cover layer situated thereon. The material of the wave-shaped layer is selected in such a way that it has a higher elongation at break than the cover layer. If a mass impact occurs and the outer cover layer is punctured, an intercept bag forms from the wave-shaped layer to dissipate the kinetic energy of the mass.
Exemplary embodiments of the present invention provide impact protection for a vehicle, in particular an aircraft, by means of which damage by stone chips, propeller ice impact, etc. may be reliably avoided, so that in particular the operational safety is not impaired, and the maintenance and repair effort for the vehicles affected by stone chip damage may be reduced.
The forces and energies that occur with stone chips (in the case of an aircraft, in particular during takeoff and landing) or propeller ice impact may be well absorbed and elastically cushioned by use of the impact protection plate according to the invention. The cushioning effect is achieved in particular by the wave-shaped layer close to the aircraft, which also has good rigidity. The impact protection plate according to the invention thus represents a type of “crumple zone” for impacting masses.
Since the critical region for stone chips on an aircraft is located in particular on the underside of the fuselage, one or more impact protection plates is/are preferably situated in this region of the aircraft fuselage. To protect from propeller ice impact, the impact protection plate is mounted in particular on the aircraft fuselage in the region of the propeller level.
Besides transport or passenger aircraft, an aircraft may also involve so-called unmanned aerial vehicles (UAVs). In addition to use on aircraft, the impact protection plate according to the invention may be used for protection of other vehicles that are subject to impact from masses, such as all-terrain vehicles, trucks, and railroad trains.
The impact protection plate according to the invention reduces repair costs for the vehicle and decrease the down times for the vehicle. The impact protection plate has very good impact-absorbing properties, with a very low weight.
The impact protection plates according to the invention may be mounted on existing vehicles without major modifications.
The impact protection plate according to the invention has the following layer structure in particular:
First Layer Close to the Vehicle (Also Referred to as “Wave Profile” Below):
This layer is composed of a fiber-reinforced plastic, and has a wave-shaped cross section with a regular pattern of alternating elevations and depressions. The transverse tensile strength of the fiber-reinforced plastic is greater than 50 MPa. The transverse tensile strength is the tensile strength of the material in the direction perpendicular to the reinforcement fibers. This transverse tensile strength is a good measure of the quality of the fiber/matrix binding within the fiber-reinforced plastic material. The selected parameter range ensures that the integrity of the layer, and thus the sought elastic effect, of this layer is maintained even under high stress from impacts. The individual elevations and depressions may in particular have a trapezoidal shape, although other shapes are also possible. The wave structure of this layer has the additional advantage that good ventilation of the interspace between the impact protection plate and the outer skin of the vehicle is ensured, so that corrosion processes at this location are prevented or at least impeded.
Second Layer Remote from the Vehicle (Also Referred to as “Cover Layer” Below):
This second layer is provided on the first layer as a cover layer. The second layer is a smooth layer having a curvature that is preferably adapted to the curvature of the aircraft structure. The second layer likewise is composed of a fiber-reinforced plastic, the elongation at break of the reinforcement fibers being greater than 3%. As a result of the high elongation at break, failure of this cover layer under the expected stresses due to impacts may be avoided with high reliability.
In one preferred embodiment, the elongation at break of the reinforcement fibers of the second layer is higher than the elongation at break of the reinforcement fibers of the first layer.
The selection of the layer thicknesses is made according to the application. In most cases, the thickness of the wave profile is less than the thickness of the cover layer. Preferred thickness ranges are as follows:
Wave profile: between 0.4 mm and 0.8 mm
Cover layer: between 0.9 mm and 2.0 mm
For the wave profile, the following combinations of fiber and matrix may be used in a particularly advantageous manner:
E-glass/PEEK
E-glass/PPS
E-glass/epoxy
S2-glass/PEEK
S2-glass/PPS
S2-glass/epoxy
Quartz glass/PEEK
Quartz glass/PPS
Quartz glass/epoxy
For the cover layer, the following combinations of fiber and matrix are particularly suited:
S2-glass/PEEK
S2-glass/PPS
S2-glass/epoxy
Quartz glass/PEEK
Quartz glass/PPS
Quartz glass/epoxy
Aramide/PEEK
Aramide/PPS
Aramide/PE
Aramide/PP
One particularly advantageous embodiment of the impact protection plate according to the invention has S2-glass/epoxy as material for both layers.
In particular for the variants containing epoxy resin matrix, the so-called VAP resin injection process, as described in European Patent Publication No. EP 1 181 149 B1, for example, is suitable as a manufacturing method. In this process, the component space defined by the outer vacuum film is divided into two subspaces by a membrane which is permeable to air but impermeable to resin.